System and method for determining vehicle position based upon light-based communication using signal-to-noise ratio or received signal strength indicator

ABSTRACT

A system and method for determining vehicle position uses light based communication (LBC) signals and a received signal strength indicator (RSSI) to determine the vehicle position. Each vehicle includes a LBC system having an array of transmitting light emitting diodes (LEDs) and an array of receiver photodiodes for transmitting and receiving pulsed light binary messages. Each LBC system has a controller coupled to the transmitter diodes and receiver diodes. The controller includes a vehicle communication module that may be executed by a processor to determine the distance. The processor models a first distance between a first transmitting LBC system and a first receiving LBC system, then models a second distance between a second transmitting LBC system and the first receiving LBC system, and then determines the distance between the first vehicle and the second vehicle using trilateration of the first distance and the second distance.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a divisional of U.S. patent application Ser.No. 15/422,559, titled “System and Method for Determining VehiclePosition Based Upon Light-Based Communication Using Signal-to-NoiseRatio or Received Signal Strength Indicator” and filed on Feb. 2, 2017,which is herein incorporated by reference in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates to light-based communication systems, andmore particularly to light-based communication systems that may be usedto determine vehicle position.

BACKGROUND

Determining the position and distance between vehicles on a roadway iscrucial for various automotive applications. Primarily in safetycritical situations, an advanced driver assistance system (ADAS) of avehicle may alert and/or assist the driver if a collision is imminent.In addition, vehicle position estimation is essential for autonomousvehicle navigation and mapping. The position of a vehicle relative toanother vehicle or roadway infrastructure provides information to theplanner and the navigation system in determining alternate routes orpotential hazards.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of a plurality of ground vehicleseach having one or more light based communication (LBC) systems, inaccordance with an embodiment of the present disclosure.

FIG. 2 illustrates a block diagram of a ground vehicle having eight LBCsystems, and showing the region of communication coverage provided bythe field of view of each LBC system, in accordance with an embodimentof the present disclosure.

FIG. 3 illustrates a block diagram showing the components of a LBCsystem, in accordance with an embodiment of the present disclosure.

FIG. 4 illustrates a block diagram of a perspective aerial view of twoground vehicles and the relative distances therebetween, in accordancewith an embodiment of the present disclosure.

FIG. 4A illustrates a block diagram of a perspective aerial view of twoground vehicles and the various regions of communication coverageprovided by the field of view generated by the LBC systems, inaccordance with an embodiment of the present disclosure.

FIG. 5 illustrates a block diagram of a perspective aerial view of twoground vehicles, with one vehicle approaching the other at a T-shapedintersection, and the region of the field of view generated by the LBCsystems, in accordance with an embodiment of the present disclosure.

FIG. 6 illustrates a methodology for determining distance between afirst ground vehicle and a second ground vehicle using trilateration, inaccordance with an embodiment of the present disclosure.

FIG. 7 illustrates a block diagram of a perspective aerial view of twoground vehicles and the various regions of communication coverageprovided by each LBC system, in accordance with an embodiment of thepresent disclosure.

FIG. 8 illustrates a methodology for determining distance between afirst ground vehicle and a second ground vehicle using a light basedcommunication digital message and a time-of-flight pulse, in accordancewith an embodiment of the present disclosure.

DETAILED DESCRIPTION

A system is disclosed for determining vehicle position with respect toanother vehicle or an infrastructure using light based communication(LBC). The system may use digital messages (for example LBC messages orother pulsed optical messages) in combination with a signal parameter ofthe digital message (such as a received signal strength indication(RSSI), signal-to-noise ratio (SNR) value), or a time-of-flight pulse toestimate the position of the vehicle. Each vehicle may be equipped withone or more LBC systems to communicate with another vehicle usingdigital messages. Each LBC system may include a transmitter, such as anarray of light emitting diodes (LEDs), and a receiver, such as an arrayof photodiodes, for transmitting and receiving LBC messages between thevehicles. Each LBC system also includes a controller having a processor,a vehicle communication module, and a time-of-flight module that areexecutable by the processor. In accordance with some such embodiments,the vehicle communication module is executed by the processor to processdata using the signal parameter (e.g., RSSI) of the LBC signal. Inaccordance with an embodiment, the time-of-flight module is executed bythe processor to process data using a time-of-flight pulse. The RSSI ortime-of-flight pulse may be used to determine the relative position ofone vehicle with respect to another, as will be appreciated in light ofthe present disclosure.

General Overview

Implementing a LBC system involves a number of non-trivial issues,particularly in communicating between vehicles. For example, somemethods for real-time communication in a connected vehicle environmentrequire broadcast transmission in an omnidirectional pattern. Dedicatedshort range communications (DSRC) data is an example broadcasttransmission in a radio-based 360-degree field and all recipientsreceive the same information. As more vehicles join the connectedvehicle network in dense traffic situations, the network may experiencecongestion and bottlenecks because every vehicle is broadcastingmessages. DRSC and other methods use GPS alone or in combination withsensors on the vehicle. GPS requires the GPS receiver on the vehicle tohave an unobstructed line-of-sight (LOS) view of at least four GPSsatellites. GPS has limitations in determining vehicle location due toestimation error (which is typically greater than 1 m, but may be 10 mor greater) and satellite obstruction (which may be caused by tunnels,parking garages, shadowing by tall buildings, etc.). There is a need fordirectional, specified messages to be transmitted and received, toestimate position of a vehicle, and provide other appropriateinformation. There is a need for positional, distance based, orproximity based communication where the communication medium itself (thelight including the LBC message) is utilized, specifically the receivedsignal strength and/or other information contained in the decoded LBCmessage.

Thus, in accordance with an embodiment of the present disclosure, asystem is provided for determining relative vehicle position usingdigital messages such as a pulsed optical signal and a signal parameter(e.g. RSSI of the LBC signal) or a time-of-flight pulse. The LBCmessages may be pulsed digital messages transmitted and received usinglight based communication. The vehicles implement LBC systems that use asignal parameter of the digital message or time-of-flight pulse todetermine the proximity and/or relative location of one vehicle withrespect to the other vehicle. In an embodiment, the LBC system includesa transmitter array of LEDs and a receiver array of photodiodes. Boththe transmitter and receiver arrays are coupled to a controller. Thetransmitter array of LEDs may be used to transmit both the digitalmessages and the time-of-flight pulse, in accordance with an embodiment.In another embodiment, the transmitter array may be used to transmit thedigital messages and a specific time-of-flight transceiver may be usedfor sending and receiving the time-of-flight pulse. The controller mayinclude a vehicle communication module and a time-of-flight module thatare executable by a processor of the controller. In one such embodiment,the vehicle communication module is executed by the processor and usestrilateration to determine the distance between two vehicles by firstmodeling a first distance between a first transmitting LBC system and afirst receiving LBC system, second modeling a second distance between asecond transmitting LBC system and the first receiving LBC system, andthen using trilateration to obtain the distance between the transmittingvehicle and the receiving vehicle based on the first distance and thesecond distance, as will be appreciated in light of the presentdisclosure. The distance may be discerned using two transmitting LBCsystems and one receiving LBC system that receives two light signalsfrom the two transmitting LBC systems.

In accordance with another embodiment of the present disclosure, thetime-of-flight module may be executed by the processor and use thedigital message and the time-of-flight pulse to determine the relativevehicle position. First, a digital message from a proximate(neighboring) vehicle is used to determine the relative angle of thatvehicle, at least approximately, as being within the angular opticalcharacteristics of the receiving light module (i.e., within a range ofangles that the receiving light module may capture). Specific digitalcontent within the header of that message may describe the location onthe body of the neighboring vehicle responsible for transmitting themessage, thus allowing the receiving vehicle to ascertain a relativeorientation of that neighboring vehicle, as will be appreciated in lightof the present disclosure. Then, a time-of-flight pulse is used tomeasure the distance between the neighboring vehicle and thetransmitting LBC system. Finally the angle and the distance together maybe used to provide a relative location of the transmitter with respectto the receiver, using a single transmitter device and a single receiverdevice, as will be appreciated in light of the present disclosure.

LBC-equipped vehicles in close proximity to each other are able toestimate vehicle pose more accurately because, as the vehicles becomecloser together, the received signal strength indicator (RSSI) becomeslarger. Thus, as one vehicle becomes closer to another vehicle, the RSSIbecomes larger, and likewise the RSSI decreases as the vehicles moveaway from each other. Thus, contrary to GPS, the accuracy improves asthe vehicles become closer together.

Similarly, by using time-of-flight pulses to estimate vehicle position,information in the digital message itself, such as the message header,may be used to discern the relative angle and orientation, and thetime-of-flight pulse provides the distance therebetween, and the angleand distance together provide the relative location of one vehicle withrespect to another. Thus, by using the SNR/RSSI or time-of-flightvalues, the relative position may be determined with improved accuracy,as will be appreciated in light of the present disclosure.

Light-Based Communication (LBC) System

FIG. 1 illustrates a block diagram of a plurality of vehicles eachhaving one or more light based communication (LBC) systems, inaccordance with an embodiment of the present disclosure. Each vehicleincludes one or more LBC systems that allow the vehicles to communicatewith each other and determine their relative positions with respect toeach other, as will be appreciated in light of the present disclosure.In this example, vehicle 110 includes a first LBC system 112, and asecond LBC system 114; vehicle 120 includes a first LBC system 122 and asecond LBC system 124; vehicle 130 includes a first LBC system 132 and asecond LBC system 134; and vehicle 140 includes a first LBC system 142and a second LBC system 144. Each of the vehicles are able tocommunicate with one another, as shown by the dashed-line arrows, usingthe LBC messages.

With advances in vehicle-to-vehicle (V2V) and vehicle-to-infrastructure(V2I) technology connected vehicles, as shown in FIG. 1, collisionavoidance strategies will require more accurate pose estimation than iscapable of being determined using a global positioning system (GPS)alone. In accordance with an embodiment of the present disclosure,light-based communication (LBC) is used to determine the relativeposition of a vehicle using a line-of-sight (LOS) signal strength, or, atime-of-flight pulse, or another signal parameter of the LBC signaltransmitted between other vehicles or another infrastructure on theroadway. In an embodiment, the received signal strength, or anotherparameter of the LBC signal, obtained by each LBC receiver may be usedin trilateration, in accordance with one or more techniques disclosedherein, to determine the position of a vehicle using the signal strengthof a given transmission from a known or locatable module. Due toinherent LOS nature of the LBC, directionality may be used to determinepose estimation along with a greater number of vehicles that arecommunicating on the vehicle network. Vehicles in close proximity toeach other, for example vehicles 110, 120, 130 and 140 shown in FIG. 1,are able to estimate vehicle pose more accurately because, as thevehicles become closer together, the received signal strength indicator(RSSI) becomes larger. Thus, as one vehicle becomes closer to anothervehicle, the RSSI becomes larger, and likewise the RSSI decreases as thevehicles move away from each other. By detecting and measuring the RSSI,the LBC transceivers are able to function independently of GPS, and asingle vehicle may include multiple LBC transceivers, thereby increasingthe robustness of the communication. Refer to FIG. 6 for one examplemethodology for determining distance using RSSI and trilateration.

In another embodiment, a time-of-flight pulse transmitted at or aroundthe same time as a LBC digital message is used to determine relativedistance of one vehicle with respect to another. For example, inresponse to a LBC digital message received from LBC system 124 ofvehicle 120, vehicle 110, and specifically LBC system 114, may send atime-of-flight pulse to the LBC system 124 of vehicle 120. The angularposition of vehicle 120 is inherently known to be within the angularreceiving optical characteristics defined by LBC system 114 (i.e.,within a range of angles that the LBC system 114 may capture). A headerof the LBC digital message from LBC system 124 of vehicle 120 may beused to discern the relative orientation of the two vehicles, and thetime-of-flight pulse may be used to measure the distance between the LBCsystem 114 and the LBC system 124, in accordance with an embodiment. Theangle and orientation from the LBC message and the distance from thetime-of-flight pulse may be used to determine the relative position ofthe vehicles, as will be appreciated in light of the present disclosure.Refer to FIG. 8 for one example methodology for determining distanceusing the light signal and the time-of-flight pulse. It will beappreciated in light of the present disclosure that the same lighttransmitter may be used to transmit the LBC digital message and thetime-of-flight pulse, or a dedicated time-of-flight light transmittermay be used for transmitting the time-of-flight pulse, and a transmitterarray of LEDs may be used to transmit the LBC message.

FIG. 2 illustrates a block diagram of a vehicle having eight LBCsystems, and showing the region of communication coverage provided bythe field of view of each LBC system, in accordance with an embodimentof the present disclosure. In accordance with an embodiment of thepresent disclosure, the transceiver systems may be designed to fitwithin the current vehicle headlamp, tail lamp, and other lightingmodule locations, in accordance with an embodiment of the presentdisclosure. Therefore, one configuration may include six to eight LBCtransceiver systems, including two to three for each of the front andrear, and an additional LBC system on each side marker light or exteriormirror. Any number of LBC systems may be provided on a vehicle,depending on the particular style or application of the vehicle, as willbe appreciated in light of the present disclosure. FIG. 2 illustratesone example LBC system placement on a vehicle, in accordance with anembodiment of the present disclosure. The LBC systems may each includean array of transmitter light emitting diodes (LEDs) and a receiverarray of photodiodes that contain specific optics to narrow and/or widenthe field-of-view (FOV) to provide directionality for communication.

The vehicle in FIG. 2 includes a center front LBC system 220, a driverfront LBC system 222, a passenger front LBC system 224, a driver sideLBC system 226, a passenger side LBC system 228, a driver rear LBCsystem 230, a passenger rear LBC system 232 and a center rear LBC system234. One or more of the LBC systems 220, 222, 224, 226, 228, 230, 232 or234 may be integrated into a headlight, taillight, exterior side mirrorlight, or other structure of the vehicle, in accordance with an exampleembodiment, or may be a separate transceiver unit positioned atappropriate locations on the vehicle. A region of communication coverageprovided in the field of view of each transceiver is shown in FIG. 2, inaccordance with an example embodiment. The center front LBC system 220has a region 240 of communication coverage, which is a relatively narrowregion provided in the field of view of the LBC system 220. The driverfront LBC system 222 has a region 242 of communication coverage, and thepassenger front LBC system 224 has a region 244 of communicationcoverage, which are both wider than the region 240 of the center frontLBC system, in accordance with an example embodiment. The driver sideLBC system 226 has a region 246 of communication coverage, and thepassenger side LBC system 228 has a region 248 of communicationcoverage, which is relatively wide, and shorter than the regions 242 and244, in accordance with an example embodiment. The side LBC systems 226and 228 provide a wider field of view which enhances V2V communicationwith adjacent vehicles. The side LBC systems 226 and 228 may also beused to assist in locating blind spots and cross traffic systems betweenadjacent vehicles. The driver rear LBC system 230 has a region 250 ofcommunication coverage, the passenger rear LBC system 232 has a region252 of communication coverage and the center rear LBC system 234 has aregion 254 of communication coverage. The center front LBC system 220and the center rear LBC system 234 have a narrow field of view (240,254) that provides long-range communication. The LBC systems within anygiven vehicle may be connected together via a vehicular network andtherefore know each other's location on the vehicle. More directly, thelocations of each vehicle's LBC systems may be factory known from thevehicle manufacturer design. The LBC systems may also communicate witheach other over a LBC bus 260, and thus may have knowledge of eachother's location on the vehicle. The distributed architecture of thevehicle network allows the LBC systems to act collaboratively asappropriate and independently when desired.

The region of communication coverage provided in the field of view of anLBC system generally refers to the area in which the specifiedtransceiver is able to communicate with another transceiver to transmitand receive light signals, in accordance with an embodiment.

FIG. 3 illustrates a block diagram showing components of an example LBCsystem, in accordance with an embodiment of the present disclosure. Eachvehicle may include one or more LBC systems to communicate with othervehicles, in accordance with an example embodiment.

An example LBC system 310 includes an array of transmission LEDs 320with appropriate optics and a receiver array of photodiodes 322 withappropriate collection optics, each coupled to a controller 324. Thearray of transmission LEDs 320 may be used to transmit light signals (orother digital messages) to a receiver LBC system of another vehicle, andmay also be used to send a time-of-flight pulse when applicable. Thereceiver array of photodiodes 322 may be used to receive light signals(or other digital messages) sent from an array of transmission LEDs ofanother vehicle, and may also be used to receive a time-of-flight pulsewhen applicable.

The controller 324 includes a vehicle communication module 326 and atime-of-flight module 328 that are each executable by a processor 330,depending upon the data analysis and processing to be performed, as willbe appreciated in light of the present disclosure. The processor 330 mayexecute the vehicle communication module 326 to measure the RSSI and usetrilateration to determine the distance between two vehicles, inaccordance with an example embodiment. Refer, for example, to FIG. 6 forone example methodology for determining distance using RSSI andtrilateration as performed by the vehicle communication module whenexecuted by the processor. The processor 330 may execute thetime-of-flight module 328 to use the light signal and the time-of-flightpulse to measure the distance between vehicles, as will be appreciatedin light of the present disclosure. Refer, for example, to FIG. 8illustrating one example methodology that may be implemented by thetime-of-flight module when executed by the processor to determine thedistance between two vehicles using the light signal and thetime-of-flight pulse. Each of the modules 326 and 328 may be stored inan appropriate memory of the LBC system and may be executable by theprocessor 330. In an embodiment, the modules 326 and 328 may include themethodology of FIG. 6 or FIG. 8 stored in memory as a series ofinstructions to be carried out when the module is executed by theprocessor 330.

The LBC light RSSI/SNR (signal-to-noise ratio) may be modeled accordingto a function to correlate the transmission distance and the receivedsignal strength. This information may be used by the vehiclecommunication module 326, executed by the processor 330, to determinethe distance between two vehicles, for example using the function below.The function below illustrates a single light-based transceiver system.The received power, P_(R), is a function of the distance, d, between theemitter and the detector, expressed in the following Free Space ModelFriis Transmission Equation, where P_(T) is the output power to thetransmitting antenna, G_(t) is the antenna gain of the transmittingantenna, G_(r) is the antenna gain of the receiving antenna, λ is thewavelength, d is the distance between the point source and the detector,and L is slit width of the wavelength:

${P_{R}(d)} = \frac{P_{T}G_{t}G_{r}\lambda^{2}}{( {4\pi} )^{2}d^{2}L}$

Free Space Model Friis Transmission Equation

In accordance with an example embodiment, G_(t), G_(r), λ and L areconstants. Thus,

$\frac{G_{t}G_{r}\lambda^{2}}{( {4\pi} )^{2}L}$can be represented as a constant k. Such that the received power, P_(R)(d) can be represented as:

${P_{R}(d)} = \frac{P_{T}k}{d^{2}}$

Radiometric models of a light point source and detector at distance d todepict irradiance (E) may be expressed as:

$E = \frac{1}{d^{2}}$

Irradiance (E) thus follows an inverse square law from a point sourceand a distance (d) between the point source and detector. Irradiance isdescribed as intensity per unit area. Refer to FIG. 4 for a diagram ofthe various triangles that may be used to determine the position of onevehicle relative to another using trilateration.

FIG. 4 illustrates a block diagram of a perspective aerial view of twoground vehicles and the relative distances therebetween, in accordancewith an embodiment of the present disclosure. The vehicle 410 includesat least LBC system 412 positioned at a driver front of the vehicle 410,LBC system 414 positioned at a passenger front of the vehicle 410, andLBC system 416 positioned at a passenger side of the vehicle 410, inaccordance with an embodiment. One or more LBC systems in addition tothose shown in FIG. 4 may be provided in accordance with an embodiment.The vehicle 420 includes at least LBC system 422 positioned at a driverfront of the vehicle 420 and a LBC system 424 positioned at a passengerfront of the vehicle 420, in accordance with an embodiment of thepresent disclosure.

By modeling the RSSI/SNR for one transceiver system, each modeling maybe replicated across at least three transceiver systems to usetrilateration to determine the position of each system relative to eachother. The trilateration calculation may be used to determine thelocation of the transceiver system that sent a particular signal. FIG. 4shows the potential location of the LBC systems on two vehicles that arecommunicating. From vehicle 410, if the passenger front LBC system 414and side LBC system 416 are communicating with the driver side LBCsystem 422 of the vehicle 420, and each of the LBC systems 414 and 416may estimate each other's absolute distance from the received powermeasured by the detectors (for example, array of photodiodes 322 shownin FIG. 3). In accordance with an example embodiment, vehicle 410 mayestimate its distance from vehicle 420 by measuring the received powertransmitted by vehicle 420. The messages transmitted from the LBCsystems may include a vehicle identifier (ID) and a transmitter locationon the vehicle, such that any vehicle receiving the messages mayidentify a given transmitter. Using the transmitter identifierinformation and received signal strength indicator, the absolutedistance between one LBC module and another LBC module may bedetermined, which may be used to determine the relative distance betweentwo vehicles. For example, the absolute distance D1 between the LBCsystem 414 and the LBC system 422 may be determined by the LBC system422 based upon the received signal strength from the signal emitted fromthe LBC system 414 (and vice versa may be determined by LBC system 414based on received signal strength form signal when emitted from LBCsystem 422), the absolute distance D2 between the LBC system 416 and theLBC system 422 may be determined by the LBC system 422 based upon thereceived signal strength from the signal emitted from the LBC system 416(and vice versa the distance D2 may be determined by LBC system 416based on received signal strength from the signal when emitted from theLBC system 422). In some embodiments, D3 may be a known distance to boththe LBC system 414 and the LBC system 416, as each LBC system may beconfigured to know the location of other LBC systems on a same vehicle,e.g. as a result of vehicle manufacturer design, which may be used toperform trilateration in accordance with the teachings of the presentdisclosure. Using these three calculations, the relative distance D4between the vehicle 410 and vehicle 420 may be calculated by forming asimple triangle between the LBC systems on vehicle 410 and vehicle 420.Note that although the absolute distances D1, D2 and D3 provide thedistance between the LBC systems, however these do not accuratelyrepresent the actual distance between vehicle 410 and vehicle 420 whichmust take into account other vehicle body features that protrude beyondthe dimensions of the LBC systems, and thus, from the absolutedistances, the approximate distance between vehicle 410 and vehicle 420may be inferred. The approximate distance thus refers to the physicaldistance inferred between two vehicles (D4) while the absolute distancerefers to the separation distance between two LBC systems. The absolutedistance between the LBC systems is used in trilateration to determinethe actual relative distance between two vehicles, as will beappreciated in light of the present disclosure.

Referring again to FIG. 4, two example cases are described as followsfor illustrative purposes. In a first example, two receivers (e.g. LBCsystem 414 and LBC system 416) receive the same LBC message that hasbeen transmitted by LBC system 422 of vehicle 420. In the first example,the message header may include information about the orientation ofvehicle 420. In a second example, two LBC messages transmitted by LBCsystem 414 and LBC system 416, respectively, from vehicle 410 are bothreceived by LBC system 422 on vehicle 420, in which case the messageheader may include specifically the distance D3.

FIG. 4A illustrates a block diagram of a perspective aerial view of twoground vehicles and the various regions of communication coverageprovided by the field of view generated by the LBC systems, inaccordance with an embodiment of the present disclosure. In this exampleembodiment, vehicle 410 includes a driver front LBC system 412, apassenger front LBC system 414, a passenger side LBC system 416, adriver rear LBC system 417 and a passenger rear LBC system 418. In thisexample embodiment, vehicle 420 includes a driver front LBC system 422,a passenger front LBC system 424, a driver side LBC system 426, a driverrear LBC system 427, and a passenger rear LBC system 428. The number ofposition estimator triangles that are formed from the communicationcoverage of the LBC systems on vehicle 410 and vehicle 420 is shown inFIG. 4A. The number of position estimator triangles may be used toprovide vehicle position measurement. An example position estimatortriangle 450 may be formed by the communication between LBC system 414,LBC system 416 and LBC system 422. An example position estimatortriangle 452 may be formed by the communication between LBC system 416,LBC system 422 and LBC system 426. An example position estimatortriangle 454 may be formed by the communication between LBC system 416,LBC system 418 and LBC system 422. An example position estimatortriangle 456 may be formed by the communication between LBC system 418,LBC system 426 and LBC system 427. As will be appreciated in light ofthe present disclosure, one or more position estimator triangles may beused to determine the relative position of one vehicle with respect toanother.

FIG. 5 illustrates a block diagram of a perspective aerial view of twoground vehicles, with one ground vehicle approaching the other groundvehicle at a T-shaped intersection, and the region of the field of viewgenerated by the LBC systems, in accordance with an embodiment of thepresent disclosure. The techniques for ground vehicle estimation usingtrilateration may be applied at a T-shaped intersection where vehicle510 is approaching vehicle 520 along a driving direction. As bothvehicle approach each other, the accuracy of estimated distances betweenvehicle 510 and vehicle 520 increase, given that the received signalstrength indicator or signal to noise ratio is a stronger signal as thevehicles become closer together. This is contrary to GPS based systems,where objects are more difficult to distinguish as they become closertogether.

In an embodiment vehicle 510 includes a LBC system 512 positioned at acenter front of the vehicle 510, a LBC system 514 positioned at apassenger front of the vehicle 510, and a LBC system 516 positioned at apassenger side of the vehicle 510. Other LBC systems may also beincluded in the vehicle 510. In an embodiment, the vehicle 520 includesa LBC system 522 positioned at a driver front of the vehicle 520, and aLBC system 524 positioned at a center front of the vehicle 520. OtherLBC systems may also be included in the vehicle 520. The vehicle 520 maydetermine its position with respect to vehicle 510 using a positionestimator triangle 530 formed by the communication between LBC system512, LBC system 514 and LBC system 524, or by a position estimatortriangle 532 formed by the communication between the LBC system 514, theLBC system 516 and the LBC system 522. Trilateration techniquesdisclosed herein may be used to determine the distance between thevehicle 510 and the vehicle 520. In accordance with this embodiment,similar to the triangles of FIG. 4A (e.g., triangles 450, 452, 454, and456) that are used in trilateration to determine the position of vehicle410 with respect to vehicle 412, the triangles 530 and 532 in FIG. 5 canbe used in trilateration to determine the position of vehicle 510 withrespect to vehicle 520. Thus, the triangles can be used in trilaterationto determine relative distance between the vehicles whether the vehiclesare side-by-side, as shown in FIG. 4A, or perpendicular to each other asshown in FIG. 5. The relative orientation, and thus relative distance,between two vehicles can be determined using the triangles throughperforming trilateration, as will be appreciated in light of the presentdisclosure.

Methodology—Trilateration Using a Signal Parameter

FIG. 6 illustrates a methodology for determining distance between afirst ground vehicle and a second ground vehicle using trilateration, inaccordance with an embodiment of the present disclosure. A first vehiclehaving an array of receiver photodiodes may receive a light signal (orother digital message) and use a signal parameter (e.g., RSSI), of thelight signal to determine the relative distance between the firstvehicle and a second vehicle that transmitted the light signal, forexample using the techniques shown in FIG. 6.

At block 610, a digital message (for example a light signal) isreceived, in accordance with an example embodiment. The digital messagemay be received at an array of receiver photodiodes, for example thereceiver photodiodes 322 in FIG. 3. The receiver photodiodes 322 may beconfigured to receive any LBC pulsed light message or similar digitalmessage. The digital messages received by a LBC system may include avehicle identifier (ID) and a transmitter location on the vehicle, suchthat any vehicle receiving the messages may identify a giventransmitter. The digital message header may include information aboutthe orientation of the vehicle, and the digital message can includeinformation indicating a distance between a first LBC system on avehicle and a second LBC system on the same vehicle (for example, eachLBC system in FIG. 4 can have knowledge of the distance D3).

At block 620, a RSSI is measured by the vehicle communication modulewhen executed by the processor, in accordance with an exampleembodiment. The vehicle communication module, for example, may bevehicle communication module 326, and is executable by the processor,for example, processor 330 in FIG. 3. The RSSI may be used by thevehicle communication module to determine an approximate distancebetween two vehicles. In an example embodiment, the RSSI is measured forat least two incoming (i.e. received) light signals that are receivedfrom two distinct transmitter devices.

At block 630, trilateration is used to determine the distance betweenthe receiving vehicle and the transmitting vehicle, in accordance withan example embodiment. Performing trilateration at block 630, in oneexample embodiment, may include blocks 630 a, 630 b and 630 c. At block630 a, a first distance between the first transmitting LBC system and afirst receiving module is modeled based on a first RSSI value of a lightsignal received from the first transmitting LBC system, in accordancewith an example embodiment. At block 630 b, a second distance between asecond transmitting LBC system and the first receiving module is modeledbased on a second RSSI value of a light signal received from the secondtransmitting LBC system, in accordance with an example embodiment. Atblock 630 c, the distance between the transmitting vehicle and thereceiving vehicle may be determined by the processor throughtrilateration based on the first distance and the second distance, aswill be appreciated in light of the present disclosure. In this exampleembodiment, the processor (for example processor 330 in FIG. 3) mayexecute the vehicle communication module (for example vehiclecommunication module 326 in FIG. 3) to measure the RSSI at block 620 anduse trilateration to determine the distance at block 630, which includesblocks 630 a, 630 b and 630 c.

The RSSI may be calculated from receiving any message, given that theRSSI is dependent upon the signal's amplitude. The position may beaccurately estimated by combining the RSSI in combination with thedecoded and processed LBC message. The precise location may becalculated for a LBC system that transmitted a signal, and also themessage may be processed and used for real time analysis and messagevalidity by the receiving vehicle.

LBC System Including a Time-of-Flight Pulse

The LBC systems shown and described herein may implement time-of-flighttechnology to determine the relative distance between two vehicles usinga single transmitter device and a single receiver device, in accordancewith an example embodiment. For example, the LBC message and thetime-of-flight pulse may be used to determine the distance between thetransmitter LBC system and the receiver LBC system, as will beappreciated in light of the present disclosure.

FIG. 7 illustrates a block diagram of a perspective aerial view of twoground vehicles and the various regions of communication coverageprovided by each LBC system, in accordance with an embodiment of thepresent disclosure. A plurality of spatially configured groups oftransmitter and receiver pairs is provided, in accordance with anexample embodiment. In this example, a 32-unit configuration composed ofeight physical LBC systems, each having four light elements aimed tospecific subsets of a solid angle. Each of the 32 elements (i.e.elements 1 a-32 a on vehicle 710 and elements 1 b-32 b on vehicle 712)includes a transmitter and a receiver having the angle, respectively, oftransmission and reception according to the area depicted in FIG. 7. Itis proposed that each transmitter may transmit a basic safety message,including a header that identifies the body-specific location of thetransmitter on the transmitting vehicle. In FIG. 7, two adjacent LBCequipped vehicles 710, 712 are interpreting each other's relativelocation. If vehicle 710 may discern from message header informationthat messages received at locations 11 a and 13 a are being transmittedfrom locations 27 b and 29 b, respectively, of vehicle 712, approximateangular location of vehicle 712 may be interpreted by vehicle 710. Ifthe transmitters of either unit 11 a or 13 a also send out atime-of-flight pulse, just before, at the same time, or just after theincoming message have been received, then the distance measured as thepulses reflect back from the other vehicle may be associated with thevehicle which sent the message (in this case, 712). Approximate angularlocation of the vehicle 712 with respect to vehicle 710 is discerned byvehicle 710 from the message transmitted by vehicle 712, specificallythe angle is known to be within the angle defined by the lightcharacteristics of the receiving unit of vehicle 710. Distance ofvehicle 712 with respect to vehicle 710 may be discerned from thetime-of-flight pulse sent from the vehicle 710. Together, the angle anddistance are sufficient to make known to vehicle 710, the relativelocation of the transmitter of vehicle 712. From header informationwithin the transmitted message, the body-specific location of thetransmitter is known, and thus, more detailed information may bediscerned about the orientation of the neighboring vehicle. This exampleshows two separate determinations of relative position, between 11 a and29 b, and between 13 a and 27 b, but in principle only one determinationis required, for example between 11 a and 29 b or between 13 a and 27 b.It will be appreciated in light of the present disclosure that even ifone channel of communication is provided between two vehicles, with oneset of angle and distance values, this is sufficient to estimaterelative position of the two vehicles.

The array of transmitting LEDs may be used to send the time-of-flightpulse in addition to the light signal(s) and the array of receiverphotodiodes may be used to receive the time-of-flight pulse in additionto the light signal(s), or a dedicated time-of-flight transceiver may beused to transmit and receive time-of-flight pulses.

Methodology—Time-of-Flight

FIG. 8 illustrates a methodology for determining distance between afirst ground vehicle and a second ground vehicle using a light basedcommunication signal and a time-of-flight pulse, in accordance with anembodiment of the present disclosure. A first vehicle having an array ofreceiver photodiodes may receive a LBC message and generate atime-of-flight pulse, and use the LBC message and the time-of-flightpulse to determine angle and distance, respectively, between the firstvehicle and a second vehicle that transmitted the LBC message. In someembodiments, the time-of-flight pulse may be received at a separatetime-of-flight transceiver component that transmits and receives atime-of-flight pulse, as will be appreciated in light of the presentdisclosure.

At block 810, a digital message or other light signal is received, inaccordance with an example embodiment. The digital message may bereceived at an array of photodiodes, for example the receiverphotodiodes 322 shown in FIG. 3. The digital messages received by a LBCsystem may include a vehicle identifier (ID) and a transmitter locationon the vehicle, such that any vehicle receiving the messages mayidentify a given transmitter. The digital message header may includeinformation about the orientation of the vehicle, and the digitalmessage can include information indicating a distance between a firstLBC system on a vehicle and a second LBC system on the same vehicle (forexample, each LBC system in FIG. 4 can have knowledge of the distanceD3).

At block 820, a time-of-flight pulse is transmitted and the associatedreflection is received, in accordance with an example embodiment. Thetime-of-flight pulse may be received at the same array of photodiodesthat receives the light signal (such as photodiodes 322 in FIG. 3) or ata separate component, such as a specific time-of-flight transceiver, inaccordance with an embodiment.

At block 830, the digital message and the time-of-flight pulse are usedby the time-of-flight module when executed by the processor to measurethe angle and distance, in accordance with an example embodiment. Theprocessor may be, for example, processor 330 shown in FIG. 3, which mayexecute the time-of-flight module 328 to determine the distance betweentwo vehicles. In accordance with an example embodiment, determining thedistance at block 830 may include blocks 830 a, 830 b, 830 c and 830 d.At block 830 a, the inherent angular characteristics of receiver opticalcollection may be used to define an angular range within which thetransmitting vehicle must be in. For example, the angular range of thereceiver may be used to determine the range of the transmitting vehicle.At block 830 b, the header from the LBC message may be used to discernthe relative orientation of the receiving vehicle with respect to thetransmitting vehicle, in accordance with an embodiment of the presentdisclosure. At block 830 c, the time-of-flight pulse may be used by theprocessor to measure an absolute distance between the receiving LBCsystem and a transmitting LBC system, in accordance with an exampleembodiment. For example, the receiving vehicle (i.e. the vehiclereceiving the LBC message) may transmit a time-of-flight pulse and,based on the speed of light and the amount of time that it takes for thepulse to reflect from the other vehicle (in some embodiments, thevehicle transmitting the LBC message) and return to the receiving LBCsystem, calculate the absolute distance time-of-flight between the twovehicles. At block 830 d, based on the relative angle of one vehicle toanother vehicle provided by the light signal, and the absolute distancebetween the vehicle and the other vehicle, the relative location of thetransmitter may be determined with respect to the receiver, inaccordance with an example embodiment. The precise location of onevehicle with respect to another may thus be determined using at leastone LBC system on a transmitting vehicle and at least one LBC system ona receiving vehicle, using the LBC message and the time-of-flight pulse,as will be appreciated in light of the present disclosure.

Numerous variations and configurations will be apparent in light of thedisclosure. For example, one example embodiment of the presentdisclosure provides a light based communication (LBC) system fordetermining vehicle position. The system includes a transmitter array oflight emitting diodes (LEDs); a receiver array of photodiodes; and acontroller coupled to the transmitter array of LEDS and to the receiverarray of photodiodes, the controller including a processor configured todetermine a relative distance between a first vehicle and a secondvehicle based on a first signal parameter of a first digital messagereceived at the receiver array of photodiodes. In some cases, the firstsignal parameter may be a received signal strength indicator (RSSI) ofthe first digital message. In some cases, the processor may be furtherconfigured to use trilateration to determine the relative distancebetween the first vehicle and the second vehicle based on the firstsignal parameter and a second signal parameter of a second digitalmessage received at the receiver array of photodiodes. In some cases,the processor may be further configured to use trilateration by modelinga first distance based on the first signal parameter, modeling a seconddistance based on the second signal parameter, and determining therelative distance between the first vehicle and the second vehicle basedon the first distance and the second distance. In some cases, the secondsignal parameter is a RSSI of the second digital message. In some cases,the first digital message may include a header that identifies a secondLBC system on the second vehicle with respect to a position of the firstLBC system on the first vehicle, and wherein the second LBC system isconfigured to transmit the first digital message. In some cases, thefirst LBC system is configured to be integrated into at least one of: adriver headlight assembly, a passenger headlight assembly, a drivertaillight assembly, and a passenger taillight assembly.

Another example embodiment of the present disclosure provides a methodfor determining vehicle position based upon light based communication(LBC). The method includes receiving, at a receiver array of photodiodesin a first LBC system of a first vehicle, a first digital message, thefirst digital message being received from a second LBC system of asecond vehicle; measuring, by a processor coupled to the receiver arrayof photodiodes, a first signal parameter of the first digital message;and using trilateration to determine a relative distance between thefirst vehicle and the second vehicle based at least in part on the firstsignal parameter of the first digital message. In some cases, usingtrilateration to determine the relative distance between the firstvehicle and the second vehicle may include receiving, at the receiverarray of photodiodes, a second digital message from a third LBC systemof the second vehicle; measuring, by the processor, a second signalparameter of the second digital message; and using the first signalparameter and the second signal parameter to determine the relativedistance. In some cases, the second signal parameter may be a RSSI ofthe second digital message. In some cases, using the first signalparameter and the second signal parameter to determine the relativedistance may include modeling a first distance between the second LBCsystem of the second vehicle and the first LBC system of the firstvehicle based on the first signal parameter; modeling a second distancebetween the third LBC system of the second vehicle and the first LBCsystem of the first vehicle based on the second signal parameter; andusing trilateration to determine the relative distance between the firstvehicle and the second vehicle based on the first distance and thesecond distance. In some cases, method may further include analyzing thefirst digital message to determine a position of the second LBC systemon the second vehicle. In some cases, the first signal parameter may bea received signal strength indicator (RSSI) of the first digitalmessage.

Another example embodiment of the present disclosure provides a computerprogram product including one or more non-transitory processor-readablemediums encoded with instructions that when executed by one or moreprocessors cause a process to be carried out for determining vehicleposition using light based communication (LBC), the process includingmeasuring a first signal parameter of a first digital message receivedby a receiver array of photodiodes in a first LBC system of a firstvehicle and received from a second LBC system of a second vehicle; andusing trilateration to determine a relative distance between the firstvehicle and the second vehicle based on the first signal parameter. Insome cases, the first signal parameter may be a received signal strengthindicator (RSSI) of the first digital message. In some cases, usingtrilateration to determine the relative distance may include receiving,at the receiver array of photodiodes, a second digital message from athird LBC system of the second vehicle; measuring a second signalparameter of the second digital message; and using the first signalparameter and the second signal parameter to determine the relativedistance. In some cases, the second signal parameter may be a RSSI ofthe second digital message. In some cases, using the first signalparameter and the second signal parameter to determine the relativedistance may include modeling a first distance between the second LBCsystem of the second vehicle and the first LBC system of the firstvehicle based on the first signal parameter; modeling a second distancebetween the third LBC system of the second vehicle and the first LBCsystem of the first vehicle based on the second signal parameter; andusing trilateration to determine the relative distance between the firstvehicle and the second vehicle based on the first distance and thesecond distance. In some cases, the process may further includeanalyzing the first digital message to determine a position of thesecond LBC system on the second vehicle

The foregoing description of the embodiments of the disclosure has beenpresented for the purposes of illustration and description. It is notintended to be exhaustive or to limit the disclosure to the precise formdisclosed. Many modifications and variations are possible in light ofthis disclosure. It is intended that the scope of the disclosure belimited not by this detailed description, but rather by the claimsappended hereto.

What is claimed is:
 1. A first light based communication (LBC) systemfor determining vehicle position, the system comprising: a transmitterarray of light emitting diodes (LEDs); a receiver array of photodiodes;and a controller coupled to the transmitter array of LEDS and to thereceiver array of photodiodes, the controller including a processorconfigured to: determine a relative distance between a first vehicle anda second vehicle based on a first signal parameter of a first digitalmessage received at the receiver array of photodiodes; and usetrilateration to determine the relative distance between the firstvehicle and the second vehicle based on the first signal parameter and asecond signal parameter of a second digital message received at thereceiver array of photodiodes.
 2. The system of claim 1, wherein thefirst signal parameter is a received signal strength indicator (RSSI) ofthe first digital message.
 3. The system of claim 1, wherein theprocessor is further configured to use trilateration by modeling a firstdistance based on the first signal parameter, modeling a second distancebased on the second signal parameter, and determining the relativedistance between the first vehicle and the second vehicle based on thefirst distance and the second distance.
 4. The system of claim 1,wherein the second signal parameter is a RSSI of the second digitalmessage.
 5. The system of claim 1, wherein the first digital messageincludes a header that identifies a second LBC system on the secondvehicle with respect to a position of the first LBC system on the firstvehicle, and wherein the second LBC system is configured to transmit thefirst digital message.
 6. The system of claim 1, wherein the first LBCsystem is configured to be integrated into at least one of: a driverheadlight assembly, a passenger headlight assembly, a driver taillightassembly, and a passenger taillight assembly.
 7. A first light basedcommunication (LBC) system for determining vehicle position, the systemcomprising: a transmitter array of light emitting diodes (LEDs); areceiver array of photodiodes; and a controller coupled to thetransmitter array of LEDS and to the receiver array of photodiodes, thecontroller including a processor configured to determine a relativedistance between a first vehicle and a second vehicle based on a firstsignal parameter of a first digital message received at the receiverarray of photodiodes, wherein the first digital message includes aheader that identifies a second LBC system on the second vehicle withrespect to a position of the first LBC system on the first vehicle, andwherein the second LBC system is configured to transmit the firstdigital message.
 8. The system of claim 7, wherein the first signalparameter is a received signal strength indicator (RSSI) of the firstdigital message.
 9. The system of claim 7, wherein the processor isfurther configured to use trilateration to determine the relativedistance between the first vehicle and the second vehicle based on thefirst signal parameter and a second signal parameter of a second digitalmessage received at the receiver array of photodiodes.
 10. The system ofclaim 9, wherein the processor is further configured to usetrilateration by modeling a first distance based on the first signalparameter, modeling a second distance based on the second signalparameter, and determining the relative distance between the firstvehicle and the second vehicle based on the first distance and thesecond distance.
 11. The system of claim 9, wherein the second signalparameter is a RSSI of the second digital message.
 12. The system ofclaim 7, wherein the first LBC system is configured to be integratedinto at least one of: a driver headlight assembly, a passenger headlightassembly, a driver taillight assembly, and a passenger taillightassembly.